Assembly for mounting a print head

ABSTRACT

An assembly for mounting a print head to a carriage. The assembly includes a mounting clamp and a lock element in addition to the print head and the carriage. The print head has at least two mounting studs and a drive element engaging screw. Both the carriage and the mounting clamp have openings therein through which the studs and the lock element engaging screw pass when effecting the assembly. The mounting clamp also has finger engaging tab members and a ratchet element which includes a resilient free end portion. In addition the stud receiving openings in the mounting clamp includes a ramp structure. In assembly, the mounting clamp is rotated by applying a torque to the tab members until the mounting studs engage the ramp structure of their respective stud receiving openings. Thereafter, the lock element engages the screw of the spring head and is tightened thereon. Both the resilient free end portion and the lock element are provided with ratchet teeth which are in engagement during the tightening operation. As a result, an audible clicking sound is generated which assures the operator that a tightening operation is taking place. In this position reverse rotation of the lock element relative to the free end portion is prevented.

United States Patent [191 Gentzlinger et a1.

1 1 Nov. 25, 1975 1 ASSEMBLY FOR MOUNTING A PRINT HEAD [75] Inventors: Richard V. Gentzlinger; Werner H.

Mailer, both of Waynesboro, Va.

[73] Assignee: General Electric Company,

Waynesboro, Va.

[22] Filed: July 18, 1974 [21] Appl. No.: 489,599

[52] U.S. Cl 197/1 R; 74/531; 248/500;

285/D1G. 13; 285/362; 403/259 [51] Int. C1. B41J 3/05 [58] Field of Search 197/1 R, 180, 186 R, 36;

24/3 R, 243 R; 74/531; 248/500; 403/259, 261, 316, 353; 285/D1G. 13, 362, 360, 376, 401, 361; 101/35, 41

Primary Examiner-Edgar S. Burr Assistant E.\aminerR. T. Rader [57] ABSTRACT An assembly for mounting a print head to a carriage. The assembly includes a mounting clamp and a lock element in addition to the print head and the carriage. The print head has at least two mounting studs and a drive element engaging screw. Both the carriage and the mounting clamp have openings therein through which the studs and the lock element engaging screw pass when effecting the assembly. The mounting clamp also has finger engaging tab members and a ratchet element which includes a resilient free end portion. In addition the stud receiving openings in the mounting clamp includes a ramp structure. In assembly, the mounting clamp is rotated by applying a torque to the tab members until the mounting studs engage the ramp structure of their respective stud receiving openings. Thereafter, the lock element engages the screw of the spring head and is tightened thereon. Both the resilient free end portion and the lock element are provided with ratchet teeth which 16 Claims, 10 Drawing Figures US. Patent Nov.-25,1975 sileetlof 3,921,780

US. Patent Nov. 25, 1975 Sheet 2 of3 3,921,780

US. Patent Nov. 25, 1975 Sheet 3 of3 3,921,780

FIG?) HGIO ASSEMBLY FOR MOUNTING A PRINT HEAD BACKGROUND OF THE INVENTION The present invention relates generally to an assembly in which a print head, in this case a matrix wire print head, is secured to a carriage. More specifically, the present invention relates to an assembly including a clamp having means to prevent the print head from becoming disengaged from the carriage while also readily facilitating removal of the print head from the carriage.

Many types of office machines are provided with print heads in order to produce an observable output. These print heads have a high degree of replacement in comparison to many of the other components of the machine. Quite frequently, special tools are needed in order to mount and replace the print head. All of this is time consuming and consequently expensive.

It would therefore be desirable to have a structure which provides a simplified means of positively affixing a print head and in particular a matrix wire print head to a carriage without the need of special tools.

OBJECTS AND SUMMARY OF THE INVENTION It is therefore, a general object of the present invention to provide an assembly for mounting a print head, and in particular a matrix wire print head, to a carriage so that the print head can be mounted and removed from the carriage in a simplified manner.

It is a more specific object of the present invention to provide an assembly having a mounting clamp for mounting a print head, and in particular a matrix wire print head, to a carriage so that the print head can be mounted and removed from the carriage in a simplified manner and so that loosening of the print head from the carriage is prevented.

It is another object of the present invention to provide an assembly having a mounting clamp for positively affixing a print head, and in particular a matrix wire print head, to a carriage without the need of special tools.

It is a further object of the present invention to provide means for audibly detecting when the print head and the carriage are sufficiently engaged to assure a tight connection.

These and other objects are accomplished according to the present invention by the provision of a mounting clamp and a lock element in assembly with the print head and carriage. The mounting clamp includes means for drawing the print head and carriage into a tight assembly, while the lock element includes a pair of ratchet teeth configured so that relative movement in only one is permitted without the application of an external force to separate the pair of ratchet teeth.

According to one embodiment, the print head is itself adapted to be mounted in accordance with the present invention by the provision thereon of at least two mounting studs and a screw element. To accommodate the mounting studs and screw element, the carriage and mounting clamp are provided with appropriate openings, with the stud openings in the mounting clamp having a ramp structure associated therewith for cooperation with the mounting studs. The mounting clamp is also provided with a ratchet detent element fonned preferably integrally with the mounting clamp and including a resilient free end portion. When assembled, the lock element engages both the print head screw and the ratchet detent element after the mounting clamp 2 has been rotated to bring the mounting studs into wedging engagement with their associated ramp structure, and is tightened onto the screw element thereby intensifying the wedgirig action which results in the final mounting of the print head to the carriage.

The lock element according to this embodiment has internal screw threads and external ratchet teeth. The threads engage the threads of the print head screw, while the ratchet teeth engage the ratchet detent element. As the lock element is advanced axially relative to the screw, it also causes the ratchet detent element to be deflected and this latter movement produces an audible clicking sound that ceases once the drive element has been tightened enough to remove any clearance between the print head, the carriage and the mounting clamp.

The matters discussed above, as well as further objects and features of the present invention, will be more clearly understood and appreciated following a consideration of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an exploded elevational view of an assembly including a print head, carriage, and print head mounting clamp in accordance with the present invention;

FIG. 2 is an elevational end view of the mounting clamp according to one exemplary embodiment of the present invention in initial engagement with the studs of the print head;

FIG. 3 is an elevational end view of the mounting clamp according to the same exemplary embodiment of the present invention shown in FIG. 2 after final engagement of the clamp with the studs of the print head;

FIG. 4 is a sectional view taken along the line 44 of FIG. 2 illustrating the relationship of the mounting studs to a portion of the mounting clamp during the initial engagement of themounting clamp and the print head;

FIG. 5 is a sectional view taken along the line 5-5 of FIG. 3 illustrating the relationship of the mounting studs to a portion of the mounting clamp during the final engagement of the mounting clamp and the print head;

FIG. 6 is a further detail view of the ratchet teeth arrangement;

FIG. 7 is an elevational end view of the mounting clamp according to another exemplary embodiment of the present invention after final engagement of the clamp with the studs of the print head;

FIG. 8 is an elevational side view of the mounting clamp according to the same exemplary embodiment of the present invention shown in FIG. 7;

FIG. 9 is a cross-sectional view taken along the line 99 of FIG. 8; and

FIG. 10 is a partial view in perspective of still another exemplary embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, there is shown a print head 10, which is one embodiment comprises a wire matrix print head, a supporting portion 12 of a movable carriage which is not further shown, a mounting clamp 14 and a ratcheted knob or locking element 16. For convenience, the mounting or supporting portion 12 forms part of a carriage which is used to support the print head and move it across a record medium and will hereinafter be referred to simply as the carriage 12.

3 These elements represent the essential elements of the assembly which embodies the structural aspect of the present invention. Further details of a print head operation are shown in the co-pending application Ser. No. 423,779, assigned to a common assignee, dated Dec. 11, l973.

The print head is relatively complex from the standpoint of its total structural configuration. Printing takes place by moving print wires of guide member 22 longitudinally and transversely'of carriage motion to impact the record medium at the remote or right hand end of member 22. Since the present invention is not, however, concerned with the print head per se but rather with the mounting of the print head, the illustration of the print head has been generalized with particulars as to its external structural configuration which are essential to the understanding of the present invention being shown in the most detail. With this in mind, it can be seen that the print head 10 includes a support member 18, shown as being of generally cylindrical configuration, which defines a transverse surface 20. From the surface there extends the guide member 22 for print wires which also serves as a carriage engaging guide which is generally convergently tapered in an outward direction from the surface 20. The guide member 22 is shown centrally located with respect to the surface 20 although this is not a requirement. Also extending from the surface 20 are preferably two diametrically disposed mounting studs 24 and a screw 26. The mounting studs 24 are shown as internally threaded to support member 18 and are in threaded engagement with screws (not shown). The studs 24 are provided with annular grooves 28 and terminal heads 30. The heads 30 have tool engaging grooves 32 extending transversely across them.

The carriage 12 comprises a generally flat surface within which a U-shaped opening 34 is formed to admit guide member 22 so that the guide member 22 extends therethrough. The carriage 12 has also further openings 36 through which the studs 24 extend and an opening 38 through which the screw 26 extends.

To clamp the print head 10 to the carriage 12 there is provided the mounting clamp 14'. For example, a thermoplastic material sold under the Trademark Lexan may be used for the mounting clamp 14.

The mounting clamp 14 is preferably molded as a one-piece circular plate having, as shown in FIG. 2, a central opening 40 through which the guide member 22 extends. The opening 40 is surrounded by a rim portion 42 within which slots 44 and 46 are formed. In addition, the rim portion 42, as shown in FIG. 2, has axially extending finger engaging tab members 48, as shown in FIG. 1, formed integrally therewith. These tab members 48 are provided to facilitate rotation of the mounting clamp 14, shown in FIG. 1. From one of these tab members there extends a ratchet detent member 50. The ratchet detent member 50, preferably formed integrally with its respective tab member, has a generally arcuately shaped resilient free end, see FIG. 2, which has ratchet teeth 52 along its top convex surface. The ratchet detent teeth 52 mesh with ratchet teeth 54 formed on the outer surface of the knurled knob 16, see FIGS. 1 and 3. The preferred configuration of the ratchet teeth 52 and 54 is shown in FIG. 6. There are two slots 44, one for each of the studs 24. The other slot 46 is provided, see FIGS. 1 and 2, to accommodate the screw 26. The slots 44 and 46 are also generally arcuate in shape. In this way, the mounting clamp 14,

FIG. 1, can be rotated between a release position (FIG. 2) and a lock position (FIG. 3). The slots 44 are furthermore key-shaped having a receiving opening 44a, from which an elongated opening 44b extends. On either side of the openings 44b and coextensive there with, there are formed in the rim portion 42, ramp edges 56. The ramp edges 56 are shown most clearly in FIGS. 4 and 5. I I

Having now identified the relevant structural aspects of the present invention, attention is now directed to the interrelationship of the various elements and their cooperation in assembly to effect simple and rapid mounting and removal of the print head 14. In this regard, reference will be made to FIGS. 2-6.

In FIGS. 2 and 4 the assembly is shown with the mounting clamp 14 in its initial unrotated release position. In this position the mounting studs 24 are received within the openings 36 of the carriage l2 and the receiving openings 44a of the slots 44 of the mounting clamp 14, and the screw 26 is received within the opening 38 of the carriage 12 and the slot 46 of the mounting clamp 14. The next stage in the assembly is to rotate the mounting clamp 14 in a clockwise direction (shown clockwise by arrow B) by applying a torque to the axially extending finger engaging tab member 48. liturin g this motion, the relationship between the studs .1 Q the screw 26 and the mounting clamp 14 changes t E shown in FIGS. 3 and 5. In particular the ramp ed s 1 enter their associated annular grooves 28 in the suit? and engage shoulders 58 defined by the terminal hillii 30. The shoulders 58 move up the ramp edges 56 during the rotation until the lock position shown in FIG. 3 is reached. This engagement securely wedges the car riage 12 between the print head 10 and the mouniir clamp 14.

In this position the knurled knob 16 is threaded i the screw 26. As the knob 16 is axially advanced alon the screw 16, the ratchet teeth 54 engage the'ratchet teeth 52 as shown in FIG. 6. These teeth a'reIso designed so that rotation in the direction of 'tightetfiin;v (clockwise as shown) of the knob 16, (direction A of FIG. 6) is permitted while rotation in the other or l'oosening direction (counterclockwise) is prevented. Dur ing the tightening rotation, the teeth engagement causes the resilient free end of the ratchet member 50 to undergo alternating deflection. This in turn generates an audible clicking sound which assures the operator that the knob 16 is being tightened in a direction to remove any clearances between the carriage 12, the print head 10 and the mounting clamp 14, thereby assuring a tight connection. The assembly is now se curely locked because counterclockwise rotation in the loos ening or counterclockwise direction is prevented by the engagement of the teeth 52 and 54.

In order to remove the print head 10 fromthe carriage 12, it is first necessary to deflect the resilient free end of the ratchet detent member 50 in the direction of the arrow C to a sufficient degree to allow counterclockwise rotation of the knob 16. Continued counterclockwise rotation of the knob 16 causesjt tobe' removed from the screw 26. When this is done,' then the mounting clamp 14 can be rotated counterclockwise by applying an appropriate torque to the fingerengaging tab members 48. In the release position shown in FIGS. 2 and 4, the print head 10 can be axially displaced and removed from the carriage l2.

Turning now to FIGS. 7-9, another embodiment of the present invention is shown according to which the ratchet teeth 62 and those formed on the ratchet member 60 is similar to that of the previously described embodiment. As can be seen from FIG. 8, the ratchet member 60 is offset from the plane of the rim portion 42. The rotation of the mounting clamp 14 to tighten the ramp edges 56 against the stud shoulders 58 also produces rotation of the ratchet member 60 relative to the mounting clamp 14 and consequently the ratchet teeth 62. This brings about engagement of the teeth 62 and those of the ratchet member 60 and locks the mounting clamp 14 in place. By lifting the ratchet member 60 out of engagement with the teeth 62, the mounting clamp 14 can be rotated in a direction to disengage the ramp from the shoulders 58 and hence the mounting clamp 14 from the print head.

Further according to this embodiment, the mounting clamp 14 is loosely captured or held to the carriage 12 by means of clips 63, which may be L-shaped projections as shown in FIG. 9, supported by and extending from the surface of the carriage 12.

In a still further embodiment according to the present invention and shown in FIG. 10, a tab 64 is provided with ratchet teeth on its back surface which engage ratchet teeth carried on the front surface of the carriage 12. The tab 64 and the ratchet toothed portion of the carriage 12 are designed to be separated when the mounting clamp is to be unclamped. This is accomplished by making one to be resilient with respect to the other as by making the tab 64 of resilient thermoplastic.

As can be seen from the above description, the existing state of the art has been advanced and there is now available a unique mounting clamp and cooperating elements which makes it possible to mount and remove a print head, and in particular a matrix wire print head, in a simple and effective manner. In addition, the mounting and removal is effected without the need of special tools and in such a manner that loosening of the mounted print head is prevented.

What is claimed is:

1. In combination, an assembly comprising:

a. a print head including an outer mounting member having at least two mounting studs and screw means connected thereto and extending outwardly therefrom;

b. a carriage including openings formed therein for the passage therethrough of said mounting studs and said screw means;

c. a mounting clamp including slots formed therein for the passage therethrough of said mounting studs and said screw means after passage through said carriage openings, with the slots through which said mounting studs pass including ramp means at one end thereof, ratchet means having a resilient free end portion and motion applying means for moving said mounting clamp between a release position and a lock position; and

d. a lock element which engages said screw means and the resilient free end portion of said ratchet means, and prevents the movement of said mounting clamp from said lock position to said release position.

2. The assembly as defined in claim 1, wherein said mounting clamp comprises a plate-like member having a generally planar surface with a central aperture surrounded by a rim portion, wherein the slots are formed in said rim portion with the slots through which the mounting studs pass being key-shaped and arcuate in their longitudinal extent having a circular receiving end and'an elongated portion extending from the receiving end, and wherein said ramp means are formed by the parallel edges of said elongated portions with said edges having an inclination relative to the planar surface of said mounting clamp.

3.'The assembly as defined in claim 2, wherein said mounting studs each include a screw member and an outer casing having an internally threaded bore, an annular groove and a head portion, and wherein the parallel edges of said ramp means associated with each of said mounting studs are received within said annular groove for engagement with said head portion.

4. The assembly as defined in claim 2, wherein said motion applying means comprises a pair of tab members which extend axially outwardly from the planar surface of said mounting clamp and transversely across said rim portion.

5. The assembly as defined in claim 4, wherein said ratchet means is mounted to said mounting clamp such that its free end extends generally parallel to the planar surface of said mounting clamp, wherein said free end is provided with an arcuate shape having teeth formed on its convex surface, and wherein said lock element comprises a cylindrical member having a threaded internal bore and teeth formed on its outer surface, which engage the teeth formed on the convex surface of said free end to effect locking of the assembly.

6. The assembly as defined in claim 5, wherein said ratchet means is mounted to one of said tab members.

7. The assembly as defined in claim 5, wherein the teeth formed on the convex surface of said free end and the teeth formed on the outer surface of said cylindrical member are mutually shaped so that relative rotation of said lock element with respect to said free end when said teeth are engaged occurs in only one direction.

8. The assembly as defined in claim 7, wherein said free end comprises a resilient material such that rota tion of said lock element relative to said free end when said teeth are engaged generates an audible indication of the rotation.

9. A mounting clamp for securing one member to a second member wherein said one member has a plurality of mounting studs connected thereto, comprising a plate-like member having a generally planar surface with a central aperture surrounded by a rim portion, said rim portion having a plurality of slots formed therein and finger engaging tab members extending axially outwardly therefrom, said slots being key-shaped and arcuate in their longitudinal extent and each having a circular end for receiving the mounting studs with i said second member nested between saidone member and said plate-like member, said slots having an elongated portion extending from the receiving end with theparallel edges of said elongated portion having an inclination relative to the planar surface, said inclined parallel edges engaging the mounting studs in a progressively tighter assembly during movement of the mounting clamp relative to the two members, ratchet means for locking the engagement of said inclined parallel edges with said mounting studs, and means for unlocking said last named engagement.

10. A mounting clamp and lock arrangement for securing one member to a second member wherein said one member has at least two mounting studs and screw means connected thereto, comprising:

a. a mounting clamp in the form of a plate-like member having a generally planar surface with a central aperture surrounded by a rim portion, said rim portion having a slot formed therein for receiving each of the mounting studs and the screw means with said second member being nested between said one member and said plate-like member, finger engaging tab members extending axially outwardly therefrom for effecting movement of said mounting clamp and ratchet means having a resilient free end portion, said slots being arcuate in their longitudinal extent with the mounting stud receiving slots being key-shaped and each having a circular end and an elongated portion extending therefrom, and with the parallel edges of said elongated portion having an inclination relative to the planar surface, said inclined parallel edges engaging the mounting studs in a progressively tighter assembly during movement of the mounting clamp relative to the two members between a release position and a lock position; and

b. a lock element which engages the screw means and the resilient free end portion of said ratchet means, and prevents the movement of said mounting clamp from said lock position to said release position.

11. The arrangement as defined in claim 10, wherein said ratchet means is mounted to said mounting clamp such that its free end extends generally parallel to the planar surface of said mounting clamp, wherein said free end is provided with an arcuate shape having teeth formed on its convex surface, and wherein said lock element comprises a cylindrical member having a threaded internal bore and teeth formed on its outer surface, which engage the teeth formed on the convex surface of said free end to effect locking of the two members with the mounting clamp.

12. The arrangement as defined in claim 11, wherein said ratchet means is mounted to one of said tab members.

13. The arrangement as defined in claim 11, wherein the teeth formed on the convex surface of said free end and the teeth formed on the outer surface of said cylindrical member are mutually shaped so that relative rotation of said lock element with respect to said free end when said teeth are engaged occurs in only one direction.

14. The arrangement as defined in claim 13, wherein said free end comprises a resilient material such that rotation of said lock element relative to said free end when said teeth are engaged generates an audible indication of the rotation.

15. In combination, a print head having a planar surface, a carriage for moving said head and having a planar surface, said carriage having a plurality of holes passing through its planar surface, a mounting clamp for securing said print head and carriage together at their planar surfaces, said print head having a plurality of mounting studs extending from its planar surface for passing through corresponding ones of said holes in said second member, each of said studs having an undercut portion near its free end to define a head with a shoulder, said clamp comprising a plurality of elongated apertures, each of said apertures comprising an enlarged opening at one end to receive the head of a respective one of said studs after passage through a respective hole in said carriage, each of said elongated apertures having associated therewith a ramp section offset from the aperture in the direction of the stud passage through the aperture and oriented substantially in the direction of the aperture elongation such that upon turning of the clamp the shoulder of each stud is caused to ride up the ramp to force the print head and carriage together, said carriage comprising ratchet teeth, said clamp having a peripheral tab portion carrying ratchet teeth for meshing with corresponding ratchet teeth of said carriage, said teeth being dimensioned to permit meshing of ratchet teeth only in the direction of clamp turning which forces the print head and carriage together, said tab and said ratchet teeth portion of said carriage being resilient relative to one another to enable manual disengagement of ratchet teeth to permit loosening of the clamp.

16. A mounting clamp for securing first and second members together at their planar surfaces wherein said second member comprises ratchet teeth and a plurality of holes passing through its planar surface and said first member has a plurality of mounting studs extending from its planar surface for passing through corresponding ones of said holes in said second member, and each of said studs has an undercut portion near its free end to define a head with a shoulder, said clamp comprising a plurality of elongated apertures, each of said apertures comprising an enlarged opening at one end to receive the head of a respective one of said studs after passage through a respective hole in said second member, each of said elongated apertures having associated therewith a ramp section offset from the aperture in the direction of the stud passage through the apertures and oriented substantially in the direction of the aperture elongation such that upon turning of the clamp the shoulder of each stud is caused to ride up the ramp to force the first and second member together, said clamp having a peripheral tab portion carrying ratchet teeth for meshing with corresponding ratchet teeth of said second member, said teeth being dimensioned to permit meshing of ratchet teeth only in the direction of clamp turning which forces the print head and carriage together, said tab being resilient to enable manual disengagement of ratchet teeth to permit loosening of the clamp. 

1. In combination, an assembly comprising: a. a print head including an outer mounting member having at least two mounting studs and screw means connected thereto and extending outwardly therefrom; b. a carriage including openings formed therein for the passage therethrough of said mounting studs and said screw means; c. a mounting clamp including slots formed therein for the passage therethrough of said mounting studs and said screw means after passage through said carriage openings, with the slots through which said mounting studs pass including ramp means at one end thereof, ratchet means having a resilient free end portion and motion applying means for moving said mounting clamp between a release position and a lock position; and d. a lock element which engages said screw means and the resilient free end portion of said ratchet means, and prevents the movement of said mounting clamp from said lock position to said release position.
 2. The assembly as defined in claim 1, wherein said mounting clamp comprises a plate-like member having a generally planar surface with a central aperture surrounded by a rim portion, wherein the slots are formed in said rim portion with the slots through which the mounting studs pass being key-shaped and arcuate in their longitudinal extent having a circular receiving end and an elongated portion extending from the receiving end, and wherein said ramp means are formed by the parallel edges of said elongated portions with said edges having an inclination relative to the planar surface of said mounting clamp.
 3. The assembly as defined in claim 2, wherein said mounting studs each include a screw member and an outer casing having an internally threaded bore, an annular groove and a head portion, and wherein the parallel edges of said ramp means associated with each of said mounting studs are received within said annular groove for engagement witH said head portion.
 4. The assembly as defined in claim 2, wherein said motion applying means comprises a pair of tab members which extend axially outwardly from the planar surface of said mounting clamp and transversely across said rim portion.
 5. The assembly as defined in claim 4, wherein said ratchet means is mounted to said mounting clamp such that its free end extends generally parallel to the planar surface of said mounting clamp, wherein said free end is provided with an arcuate shape having teeth formed on its convex surface, and wherein said lock element comprises a cylindrical member having a threaded internal bore and teeth formed on its outer surface, which engage the teeth formed on the convex surface of said free end to effect locking of the assembly.
 6. The assembly as defined in claim 5, wherein said ratchet means is mounted to one of said tab members.
 7. The assembly as defined in claim 5, wherein the teeth formed on the convex surface of said free end and the teeth formed on the outer surface of said cylindrical member are mutually shaped so that relative rotation of said lock element with respect to said free end when said teeth are engaged occurs in only one direction.
 8. The assembly as defined in claim 7, wherein said free end comprises a resilient material such that rotation of said lock element relative to said free end when said teeth are engaged generates an audible indication of the rotation.
 9. A mounting clamp for securing one member to a second member wherein said one member has a plurality of mounting studs connected thereto, comprising a plate-like member having a generally planar surface with a central aperture surrounded by a rim portion, said rim portion having a plurality of slots formed therein and finger engaging tab members extending axially outwardly therefrom, said slots being key-shaped and arcuate in their longitudinal extent and each having a circular end for receiving the mounting studs with said second member nested between said one member and said plate-like member, said slots having an elongated portion extending from the receiving end with the parallel edges of said elongated portion having an inclination relative to the planar surface, said inclined parallel edges engaging the mounting studs in a progressively tighter assembly during movement of the mounting clamp relative to the two members, ratchet means for locking the engagement of said inclined parallel edges with said mounting studs, and means for unlocking said last named engagement.
 10. A mounting clamp and lock arrangement for securing one member to a second member wherein said one member has at least two mounting studs and screw means connected thereto, comprising: a. a mounting clamp in the form of a plate-like member having a generally planar surface with a central aperture surrounded by a rim portion, said rim portion having a slot formed therein for receiving each of the mounting studs and the screw means with said second member being nested between said one member and said plate-like member, finger engaging tab members extending axially outwardly therefrom for effecting movement of said mounting clamp and ratchet means having a resilient free end portion, said slots being arcuate in their longitudinal extent with the mounting stud receiving slots being key-shaped and each having a circular end and an elongated portion extending therefrom, and with the parallel edges of said elongated portion having an inclination relative to the planar surface, said inclined parallel edges engaging the mounting studs in a progressively tighter assembly during movement of the mounting clamp relative to the two members between a release position and a lock position; and b. a lock element which engages the screw means and the resilient free end portion of said ratchet means, and prevents the movement of said mounting clamp from said lock position to said release position.
 11. The arrangement as defined in claim 10, wherein said ratchet meAns is mounted to said mounting clamp such that its free end extends generally parallel to the planar surface of said mounting clamp, wherein said free end is provided with an arcuate shape having teeth formed on its convex surface, and wherein said lock element comprises a cylindrical member having a threaded internal bore and teeth formed on its outer surface, which engage the teeth formed on the convex surface of said free end to effect locking of the two members with the mounting clamp.
 12. The arrangement as defined in claim 11, wherein said ratchet means is mounted to one of said tab members.
 13. The arrangement as defined in claim 11, wherein the teeth formed on the convex surface of said free end and the teeth formed on the outer surface of said cylindrical member are mutually shaped so that relative rotation of said lock element with respect to said free end when said teeth are engaged occurs in only one direction.
 14. The arrangement as defined in claim 13, wherein said free end comprises a resilient material such that rotation of said lock element relative to said free end when said teeth are engaged generates an audible indication of the rotation.
 15. In combination, a print head having a planar surface, a carriage for moving said head and having a planar surface, said carriage having a plurality of holes passing through its planar surface, a mounting clamp for securing said print head and carriage together at their planar surfaces, said print head having a plurality of mounting studs extending from its planar surface for passing through corresponding ones of said holes in said second member, each of said studs having an undercut portion near its free end to define a head with a shoulder, said clamp comprising a plurality of elongated apertures, each of said apertures comprising an enlarged opening at one end to receive the head of a respective one of said studs after passage through a respective hole in said carriage, each of said elongated apertures having associated therewith a ramp section offset from the aperture in the direction of the stud passage through the aperture and oriented substantially in the direction of the aperture elongation such that upon turning of the clamp the shoulder of each stud is caused to ride up the ramp to force the print head and carriage together, said carriage comprising ratchet teeth, said clamp having a peripheral tab portion carrying ratchet teeth for meshing with corresponding ratchet teeth of said carriage, said teeth being dimensioned to permit meshing of ratchet teeth only in the direction of clamp turning which forces the print head and carriage together, said tab and said ratchet teeth portion of said carriage being resilient relative to one another to enable manual disengagement of ratchet teeth to permit loosening of the clamp.
 16. A mounting clamp for securing first and second members together at their planar surfaces wherein said second member comprises ratchet teeth and a plurality of holes passing through its planar surface and said first member has a plurality of mounting studs extending from its planar surface for passing through corresponding ones of said holes in said second member, and each of said studs has an undercut portion near its free end to define a head with a shoulder, said clamp comprising a plurality of elongated apertures, each of said apertures comprising an enlarged opening at one end to receive the head of a respective one of said studs after passage through a respective hole in said second member, each of said elongated apertures having associated therewith a ramp section offset from the aperture in the direction of the stud passage through the apertures and oriented substantially in the direction of the aperture elongation such that upon turning of the clamp the shoulder of each stud is caused to ride up the ramp to force the first and second member together, said clamp having a peripheral tab portion carrying ratchet teeth for meshing with corresponding ratchet teeth of said second Member, said teeth being dimensioned to permit meshing of ratchet teeth only in the direction of clamp turning which forces the print head and carriage together, said tab being resilient to enable manual disengagement of ratchet teeth to permit loosening of the clamp. 